Blender cycles texture flickering issue when rendering unique simple solid
You have a double surface issue. you made the object in edit mode I presume. and 2 times!
ALWAYS check for face orientations:

quick fix:
on edit mode, select all with A then press M and merge distance.
and recalculate your normal after that:
https://docs.blender.org/manual/en/latest/modeling/meshes/editing/mesh/normals.html#recalculate